Effects of nucleus accumbens core and shell lesions on autoshaped lever-pressing.

Certain Pavlovian conditioned stimuli (CSs) paired with food unconditioned stimuli (USs) come to elicit approach and even consumption-like behaviors in rats (sign-tracking). We investigated the effects of lesions of the nucleus accumbens core (ACbC) or shell (ACbS) on the acquisition of sign-tracking in a discriminative autoshaping procedure in which presentation of one lever CS was followed by delivery of sucrose, and another was not. Although we previously found that bilateral lesions of the whole ACb disrupted the initial acquisition of sign-tracking, neither ACbC or ACbS lesions affected the rate or percentage of trials in which rats pressed the CS+. In addition, detailed video analysis showed no effect of either lesion on the topography of the sign-tracking conditioned response (CR). These and other results from lesion studies of autoshaping contrast with those from previous sign-tracking experiments that used purely visual cues (Parkinson et al., 2000a,b), suggesting that the neural circuitry involved in assigning incentive value depends upon the nature of the CS.